Dental procedures often require the dentist to remove decay from a tooth. The removal of tooth decay is commonly known as tooth reduction and may involve cutting, excavating, or etching of the enamel and dentin layers of the tooth. During these procedures, the dentist often must also remove all or part of associated tooth structures such as fillings, crowns, caps, composites, and the like.
Previously, dentists have used drills to reduce teeth. Drills, however, generate heat, vibration, and noise which cause discomfort in the patient. In addition, the dentist cannot precisely observe the progress of the drill as it cuts the tooth, increasing the likelihood that the drill may inadvertently cut through the dentin layer and into the sensitive pulp layer of the tooth, causing acute pain in the patient. As a result, anesthesia is typically used during tooth reductions performed using a drill.
More recently, air abrasion techniques have been used as a substitute for drilling. Air abrasion systems generally introduce abrasive material to a pressurized jet of air which is then directed toward the appropriate tooth area of the patient. Similar to sand-blasting, the pressurized air causes the abrasive material to strike the tooth at a sufficient velocity to remove a surface layer of the tooth. Air abrasion does not create the heat, vibration, and noise problems associated with drills. Furthermore, the dentist may more precisely control the area and depth of tooth material being removed, thereby reducing the amount of pain to the patient and often eliminating the need for anesthesia.
It has been found that different abrasive materials are more suited for particular dental procedures. For example procedures requiring relatively large amounts of tooth material to be removed can be performed more quickly with larger size abrasive particles. Procedures requiring relatively small amounts of tooth removal, and perhaps a greater degree of precision, are better performed with a smaller abrasive particle size. Accordingly, air abrasion systems are known, such as the apparatus described in Goldsmith et al., U.S. Pat. No. 5,334,019, which have a plurality of chambers. Each chamber in such a system supplies a different abrasive material. An air abrasion system which delivers more than one size particle allows the dentist to perform a full range of dental procedures by merely selecting the appropriate particle size.
Unfortunately, conventional air abrasion systems do not effectively switch between different particle sizes. When a conventional system stops delivering abrasive material to the patient, some of the abrasive material remains in the system, hose, and hand piece. The residual material restricts flow through the system so that, when the system subsequently attempts to deliver more abrasive material, the system must also push the residual material out the hand piece. As a result of the additional load created by the residual material, the subsequent blast delivered by the system has relatively low velocity and does not effectively reduce the tooth.
Residual abrasive material is even more detrimental when the dentist switches between abrasive materials. In that situation, the subsequent blast delivered by the system not only has a low velocity, but also contains the previous abrasive material which may not be suited for the particular procedure being performed by the dentist. Initial delivery of the wrong abrasive material after switching is known as "crosstalk", and is a significant disadvantage when using conventional air abrasion systems.
A further problem with conventional abrasion systems is backflow of biological material into the dispensing chambers. The abrasion hand piece is placed inside the patient's mouth during dental procedures. When abrasive material is not being delivered by the abrasion system, air pressures in the system allow biological material, such as blood, saliva, and portions of tooth, from the patient to flow back through the hand piece and hose and into the abrasion system. It is possible for the backflow material to reach the dispensing chambers, thereby clogging powder delivery and presenting a potential health risk to subsequent patients.
A significant problem with typical abrasion systems is clogging of the abrasive material due to moisture in the system. Abrasion systems typically deliver an abrasive powder material from a dispensing chamber through small diameter tubing. These systems are further typically connected to a compressor for supplying pressurized air to the chamber. The air supplied by the compressor has a water content which passes through the compressor and into the chambers. The moisture from the air, however, causes particles of abrasive powder to clump, thereby clogging the system.
Abrasion systems are known which use heating apparatus to address the moisture problem. The heating apparatus is used to increase the temperature in the system, thereby drying the abrasive powder. Such systems are inadequate, however, in that the moisture returns to the powder when the system subsequently cools or undergoes a pressure change. Furthermore, such systems require a start-up period during which the heating apparatus warms before the system may be used.
Conventional air abrasion systems further have an overly high number of fittings and tubing sections which form passages for the pressurized air through the system. The number of fittings increases the difficulty and amount of time needed to assemble the systems and introduces a number of potential air leaks.
An additional problem with the use of air abrasion systems is the efficient evacuation of used or spent abrasive material. After impacting upon the tooth, the abrasive material either collects in the patient's mouth or deflects back out into the area surrounding the patient's mouth. Conventional methods for collecting spent abrasive material typically involve a vacuum-type system having a filter. The filter, however, rapidly clogs with abrasive material and other larger debris such as portions of tooth and gum material. The clogged filter restricts air flow through the system, thereby lowering suction capacity. Conventional abrasion systems further require frequent filter changes due to the clogging.